There are known fiber application machines, commonly called fiber placement machines, for the application by contact onto a laying up tool, such as a male or female mold, of a wide band formed of several continuous flat fibers, of ribbon type, dry or impregnated with thermosetting or thermoplastic resin, in particular carbon fibers consisting of a multitude of carbon threads or filaments.
These machines are used to produce preforms formed of several superposed plies, each ply being formed by laying up onto the mold of one or more bands side by side. In the case of a layup of fibers pre-impregnated with thermoplastic or thermosetting resin, typically of a quantity of at least 40% in weight, the pre-impregnated preform obtained after laying up is hardened or polymerized by passing it through an oven to obtain a composite material part. In the case of so-called dry fibers, which are not pre-impregnated with resins, the fibers comprise a reduced quantity of so-called bonding resin, also called a binder, generally a thermoplastic resin, in a quantity of less than or equal to 5% in weight, to give a tackiness to the fibers during the laying up. After laying up, the so-called dry preform is subjected to a resin injection or infusion operation before the curing step.
These machines, such as described in the patent document WO2006/092514, typically comprise a fiber application head, a system for moving the head, fiber storage means, and fiber conveying means for conveying the fibers from the storage means to the head. The head typically comprises an application roll, also called a compacting roll, intended to come into contact with the mold for applying the band, and means for guiding the fibers on the application roll.
The head generally further comprises a heating system for heating the fibers. The compacting roll presses the band of fibers against the application surface of the mold, or against the band (s) of fibers previously applied, in order to facilitate the adhesion of the applied bands to each other, as well as to progressively discharge the air trapped between the laid bands. The heating system ensures the heating of the bands of fibers to be applied, and/or of the mold or bands already applied upstream of the compacting roll, just before the compacting of the band, in order to at least soften the pre-impregnation resin or bonding resin, and thus promote adhesion of the bands to one another.
In the case of thermosetting resins, the pre-impregnated fibers are simply heated to soften them, typically at temperatures in the order of 40° C. The heating system typically comprises an infrared heating system comprising one or more infrared lamps.
In the case of thermoplastic resins, the fibers pre-impregnated or having a binder must be heated at higher temperatures, at least up to the resin melting temperature, being in the order of 200° C. for nylon type resins, and up to about 400° C. for PEEK type resins.
To achieve these higher temperatures, hot air torch systems have been proposed, and more recently laser type heating systems to achieve accurate and concentrated heating. Due to the higher heating temperatures, the fiber placement heads are typically equipped with metallic compacting rolls, resistant to heat, which can furthermore be cooled by the interior via a water circuit. To be able to adapt itself to the profile of the application surface, segmented metallic compacting rolls have been proposed, comprising several roll segments independently mounted side by side on a same axle, each segment being radially moveable and in an independent manner, and being elastically biased against the application surface. These segmented metallic rolls have proven however to be complex in structure and implementation.
Flexible rolls formed from a so-called high temperature elastomer, including a thermal stabilizer, are also used. To cool them, it has been proposed to equip the placement heads with a cooling system capable of delivering an air flow to cool the roll from the outside or from the inside, as described in patent document FR 2948058. Despite these cooling systems, the flexible rolls can have the tendance to deteriorate rapidly in the case of the use of thermoplastic resins.